Wireless communication systems allow wireless devices to communicate without the necessity of wired connections. Because wireless systems have become so integrated into daily life, there is a growing demand for wireless communication systems that support multimedia services such as speech, audio, video, file and web downloading, and the like. Various wireless communication protocols and transmission control mechanisms have been developed to meet the growing demands of multimedia services over wireless communication networks and to improve the performance of these multimedia services. An exemplary transmission control mechanism for transmitting packet data units (PDUs) in wireless systems is Hybrid Automatic Repeat Request (HARQ).
Generally, there are two main variants of HARQ retransmission mechanisms supported in a wireless system employing W-CDMA: incremental redundancy (IR) and chase combining. Using IR, a physical (PHY) layer will encode the HARQ packet thereby generating several versions of encoded subpackets, called Redundancy Versions (RVs). In IR, the encoding process may include the steps of encoding, interleaving, and puncturing, and multiple RVs may be created when the HARQ packet passes through these steps. For chase combining, the PHY layer also encodes the HARQ packet. However, only one version of the encoded packet is generated. Thus, in chase combining, the transmitting device retransmits the same encoded version every time retransmission is required.
FIG. 1 is a diagram illustrating point-to-multipoint (PTM) transmissions of HARQ PDUs (i.e., a single transmitting device transmits to multiple receiving devices). In PTM transmission, a transmitting device 110 transmits encoded PDUs, also called redundancy versions, using a common radio resource, and instructs a group of receiving devices 120, e.g., receiving devices 120a, 120b, and 120c, to receive the transmitted encoded PDUs simultaneously with one another. PTM transmissions may be used by transmitting device 110 for broadcasting and/or multicasting of packet data.
Generally, one impact to channel quality is the distance between the transmitting device and the receiving device. Therefore, transmitting device 110 may evaluate channel conditions between itself and each of receiving devices 120 and, based on the evaluated channel quality information, determine a desired number of encoded PDUs needed for every receiving device 120 in the group of receiving devices 120 within its broadcast range to successfully receive the encoded data. Thus, when performing PTM transmissions, transmitting device 110 may cause every receiving device 120 to receive the same number of encoded PDUs. Specifically, in order to provide every receiving device 120 with an opportunity to correctly receive and decode the packet data, transmitting device 110 may send a greater number of encoded PDUs in order to enable the successful reception of the packet data by every member of the group of receiving devices 120.
For example, referring to FIG. 1, although receiving devices 120a and 120b may be capable of receiving fewer encoded PDUs to successfully decode the data (e.g., receiving device 120a may require only one encoded PDU a0, and receiving device 120b may require two encoded PDUs a0 and a1), receiving device 120c may have poorer channel quality and thus may require a greater number of encoded PDUs (e.g., receiving device 120c may require encoded PDUs a0 through aN-1). However, to ensure that all receiving devices 120 are able to receive and decode PTM transmissions, transmitting device 110 may be required to encode and modulate PTM transmissions to generate a larger number of encoded PDUs, e.g., a0, through aN-1, and receiving devices 120 may be required to receive and decode that larger number of encoded PDUs, which may greater than needed to successfully decode the PTM data. As a result, receiving devices 120 having good channel conditions may use unnecessary battery power to receive and decode the PTM data.
Because transmitting device 110 may not prepare a set of subpackets that are most appropriate to all the receiving devices 120 it serves, there may be significant delays and wasted resources for both the transmitting device 110 and any receiving devices 120. Furthermore, because transmitting device 110 may use a greater number of packets, or less efficiently modulated and coded subpackets, than are necessary for some or many of the receiving devices 120 in its range, receiving devices 120 that could successfully receive data transmitted using fewer coded subpackets may unnecessarily spend resources receiving and decoding a greater amount of data.
The disclosed embodiments are directed to overcoming one or more of the problems set forth above.